Fix "451 4.7.1": Your mail was greylisted and temporarily deferred

Bouncing with 451 4.7.1? It means your mail was greylisted and temporarily deferred.

How to fix it

Ensure your server retries; legitimate mail passes greylisting on retry.

Prevent it long-term

• Authenticate with SPF, DKIM and DMARC.
• Send from a dedicated, reputation-clean IP.
• Keep bounce and complaint rates low.

How Rainmail helps

Rainmail sends from your own domain on a dedicated, isolated IP with SPF, DKIM, DMARC, reverse-DNS and managed warm-up handled for you, plus an AI that watches your list health and deliverability — and it welcomes the senders Amazon SES, SendGrid and Mailchimp reject, from $8. Run the free 10-second checker or see plans.